This invention relates to a hydraulic damper for a motor vehicle, and to a method of forming such a hydraulic damper. By hydraulic damper is meant a suspension strut or shock absorber.
Attention is drawn to related U.S. patent application Ser. No. 08/324,146 entitled "Spin Closing Apparatus and Method", Ser. No. 08/324,147 entitled "Hydraulic Damper" and Ser. No. 08/380,549 entitled "Hydraulic Damper"), filed concurrently with the present application.
A hydraulic damper for use in the suspension system of a motor vehicle typically comprises a tube; a piston sealably slidably mounted in the tube and attached to a piston rod, the piston separating a compression chamber from a rebound chamber within the tube; a compression stroke valve mounted on the piston which allows fluid flow from the compression chamber to the rebound chamber; and a rebound stroke valve mounted on the piston which allows fluid flow from the rebound chamber to the compression chamber. The piston rod extends out of the tube at one end thereof, and is sealably slidably mounted in that one end. Such hydraulic dampers either comprise an inner tube and an outer tube (sometimes referred to as a twin tube damper) in which the piston sealably slides in the inner tube, or comprise a single tube (sometimes referred to as a monotube damper).
It is usual practice to form the or each tube of a hydraulic damper by rolling a sheet of steel and welding together the adjacent longitudinal edges. External parts, such as the spring seat and the mounting bracket or steering knuckle, which are also formed from steel, are then welded to the single tube or the outer tube. The other end of the tube is sealed closed by welding on an end plate or by arc-heating and rolling the tube end, and the internal components of the suspension strut (such as those mentioned above) are inserted into the tube by way of the one end thereof, which is then sealed closed. The use of several welding steps has disadvantages in that welds are time consuming operations. Further, welds are susceptible to corrosion. Still further, the use of steel has disadvantages with regard to weight.